The mechanisms of the sputter induced orientation change in YBa2Cu3O7-x(YBCO) films grown on MgO (001) substrates by pulsed organometallic beam epitaxy (POMBE) are investigated by x-ray diffraction, Rutherford backscatter spectroscopy (RBS), cross-section TEM (XTEM) and microanalysis. It is found that the W atom implantation concurring with the ion sputtering plays an important role in effecting the orientation change. This implantation changes the surface structure of the substrate and induces an intermediate layer in the initial growth of the YBCO film, which in turn acts as a template that induces the orientation change. It seems that the surface morphology change caused by ion sputtering has only a minor effect on the orientation change.

A set of 45° [001] bi-epitaxial YB_2Cu_3O_7− x thin film grain boundaries was studied to compare the effects of the microstructure on transport properties. The grain boundaries were made using two different deposition techniques: pulsed laser deposition (PLD) and pulsed organometallic beam epitaxy (POMBE). The transport properties were highly dependent on the specific growth conditions used, resulting in both fully resistive and superconducting grain boundaries. Subsequent microstructural analysis of the measured boundaries showed that both types (superconducting and resistive) meandered on the length scale of hundreds of nanometers. The major structural difference between the boundaries was at the atomic scale where the resistive boundary had a 1 nm wide disordered region. The direct correlation of microstructure to transport properties demonstrates the importance of the atomic scale structure in the resulting transport behavior.

The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45° oriented growth to the 0° oriented growth.

MgO films and YBa2Cu3O7−δ/MgO multilayer films were developed with the pulsed organometallic beam epitaxy (POMBE) growth technique, and grain boundary junctions were fabricated from the films to demonstrate the utility of the multilayers. High-quality MgO films were grown on LaAlO3 substrates by POMBE using a Mg(dpm)2 precursor. MgO crystallinity, as assessed by x-ray diffraction rocking curves, improved with the use of CuOx or YBa2Cu3O7−δ buffer layers. YBa2Cu3O7−δ films grown on the MgO layer by POMBE exhibited a Tc0 of 83 K and a Jc (12 K) exceeding 106 A/cm2 for applied magnetic fields up to 3 × 104 G. Grain boundary junctions were formed by growing YBa2Cu3O7−δ on MgO films that had been pretreated with a simple sputtering technique. This sputtering induces a controlled, 45°grain boundary in subsequently deposited YBa2Cu3O7−δ films. The resulting boundary showed weak-link current-voltage behavior and an IcRn product of 52 μV at 10 K, demonstrating that sputter-induced grain boundary junctions are compatible with multilayer technology.

It is well known that high-angle grain boundaries in YBa2Cu3O7−x (YBCO) show weak-link effects and behave as Josephson junctions. This kind of grain boundary junction (GBJ) has potential applications in magnetic field measurement and electronic devices. This work studies the microstructure of artificially made GBJs in YBCO films on (001) MgO and the mechanism of the boundary formation, with the goal to improve the GBJ quality and obtain a better understanding of the junctions’ transport properties.Ion-sputter-induced epitaxy is used to form YBCO films with isolated 45° [001] tilt grain boundaries. Prior to YBCO film growth the (001) MgO substrate is selectively sputtered by a low energy Ar ion beam. A portion of the substrate remains non-sputtered by protecting the surface with a patterned photoresist mask. After removing the mask, a YBCO film is grown on the substrate using pulsed organometallic molecular beam epitaxy (POMBE). Under suitable conditions single crystal YBCO c-axis films can be reproducibly obtained in both the sputtered and non-sputtered regions. The orientation between the films and the substrate has been examined by both x-ray diffraction and electron diffraction. The in-plane orientation relation is [110]YBCO//[100]MgO on the non-sputtered epitaxially polished MgO and [100]YBCO//[100]MgO on the sputtered MgO. Thus, 45° tilt boundaries are formed in the film at the boundary between the sputtered and non-sputtered substrate regions.

Tilt grain-boundary junctions with a 45° [001] misorientation were formed in YBa2Cu3O7−x (YBCO) thin films grown by pulsed organometallic beam epitaxy on (100) MgO substrates. The junctions were introduced at predetermined locations due to a modification of the orientation relation between the thin film and substrate following a low-energy argon ion irradiation of specific areas of the substrate surface prior to film deposition. Rutherford backscatter spectrometry and certain surface features observed by atomic force microscopy indicate that implantation of ions is necessary to cause the modified epitaxy. The low-temperature transport characteristics of individual isolated grain boundaries were determined by electromagnetic characterizations of the junction behavior. The same grain boundaries were examined by transmission electron microscopy and high-resolution electron microscopy and it was found that the boundaries are for the most part free of precipitates and well structured at the atomic scale. Regardless of the average grain boundary inclination, asymmetric (110)(100) facets dominate the microstructure of the junctions. Possible mechanisms for epitaxy modification and the transport properties in relation to the observed microstructure are discussed.

Individual 45{degrees} [0011] tilt grain boundaries in Y{sub l}Ba{sub 2}Cu{sub 3}O{sub 7{minus}x} thin films grown on biepitaxial substrates were studied. The thin films were grown using both pulsed organometallic beam epitaxy (POMBE) and laser ablation. Transport characteristics of the individual grain boundaries were measured including resistance -- temperature (R-T) and current -- voltage (I-V) dependencies with and without an applied magnetic field. In order to elucidate possible structural origins of the differences in transport behavior, the same grain boundaries which were electrically characterized were subsequently thinned for electron-microscopy analysis. Transmission-electron-microscopy and high-resolution-electron-microscopy were used to structurally characterize the grain boundaries. The macroscopic and microscopic structures of two boundaries, a nominally resistive and a superconducting grain boundary, are compared. Work supported by the National Science Foundation Office of Science and Technology Centers, under contract {number_sign}DMR 91-20000 (BVV, DBB) and the US Department of Energy, Basic Energy Sciences-Materials Science, under contract {number_sign}W-31-109-EN(S-38 (KLM).

Grain boundaries can act as weak links in the high T/sub c/ materials. If properly controlled, these grain boundaries can be used in various device applications. We have been able to reproducibly form 45/spl deg/ [001] tilt grain boundary junctions in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films. The films were grown-on MgO substrates using a pre-growth substrate treatment. A low energy broad beam argon ion source was used to irradiate a select region of (100) MgO substrates. The film on the milled portion of the substrate grows predominantly with a grain orientation rotated 45 degrees about the c-axis with respect to the grain on the unmilled portion. Backscattered electron Kikuchi patterns have been used to confirm that the rotation occurs across the entire milled portion of the substrate. Transport properties of these films are discussed and related to high resolution electron microstructural and microchemical analyses of the grain boundaries. This technique has potential use in device applications as a method for controlled grain boundary engineering.< >

A low voltage argon ion sputter technique was used to form grain boundary junctions in YBa2Cu3O7−x thin films on MgO. The YBa2Cu3O7−x thin film grown on a pre‐sputtered region of MgO was rotated 45° about the [001] axis relative to the YBa2Cu3O7−x thin film grown on an adjacent unsputtered region of the substrate. YBa2Cu3O7−x thin films were grown using pulsed organometallic beam epitaxy (POMBE). The current‐voltage and resistance‐temperature characteristics of individual grain boundary junctions demonstrated weak‐link‐type behavior. Sputter‐induced 45° grain boundary junctions are advantageous in device applications because they are planar and simple to form in many configurations.

We have investigated the normal-state resistance and the excess low-frequency (1/f) noise in 45\ifmmode^\circ\else\textdegree\fi{} tilt [001] grain-boundary junctions in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ thin films. A characteristic temperature dependence of the resistance fluctuations and a linear temperature dependence of the grain-boundary resistance (with a negative temperature coefficient) emerge as common features. These observations are quantitatively compared with a model of many, parallel conduction paths across the boundary, taking into account both temperature-independent and thermally activated transport processes.